THE PATTERN OF CATECHOLAMINE RESPONSE TO BURST ACTIVITY IN LEOPARD FROGS, RANA-PIPIENS

It is well known that burst activity causes a rapid breakdown of muscl e glycogen and extensive accumulation of lactate in frogs. During reco very, it has been shown that lactate is nearly totally recycled into m uscle glycogen. Since catecholamines are likely to play some role in t he regulation of postexercise repletion of muscle glycogen, the patter n of catecholamine response was assessed in frogs during intense physi cal activity and the ensuing recovery period. Chronically cannulated f rogs were forced to swim until exhaustion, and serial blood samples we re taken at regular time intervals for the measurements of catecholami nes. The pattern of changes in plasma and muscle lactate and glucose a nd muscle glycogen during and after burst activity is similar to that reported in previous studies using noncannulated frogs, a result which indicates that the animals recover well from the surgical trauma asso ciated with cannulation. The concentrations of plasma catecholamines i n frogs at rest are comparable to those measured in other amphibians, and the levels of plasma epinephrine in resting frogs are much higher than those of norepinephrine. Burst activity causes a marked increase in plasma catecholamines, with higher levels reached by epinephrine. D uring recovery, the concentration of plasma catecholamines returns to normal within 30 min. Although this pattern of catecholamine response to intense physical activity may be favorable to the repletion of musc le glycogen postexercise, it remains to be clarified how critical the low levels and fast reduction in plasma catecholamines are for optimum glycogen resynthesis. (C) 1994 Academic Press, Inc.